The present disclosure relates, generally, to transparent conducting materials (“TCMs”) and, more particularly, to hybrid TCMs including a polycrystalline film that is “percolation doped” with conductive nanostructures.
Since resistivity and transmittance are often fundamentally constrained by the intrinsic properties of a material, developing TCMs with both low sheet resistance (e.g., RS<10 Ω/sq) and high transmittance (e.g., T>90%) has been a persistent challenge. Various metal-doped oxides, such as indium tin oxide (“ITO”), are currently used in many commercial applications. A suitable replacement for ITO is desired, however, for at least the following reasons: the limited availability and high-cost of indium, increasing brittleness with aging, chemical instability under acid/base conditions, poor transmittance in the near infrared, and/or metallic-ion diffusion from ITO into thin barrier layers that may result in parasitic leakage. These and other problems make ITO-based technologies non-ideal for applications such as thin-film photovoltaics (“PVs”), flexible electronics, touch-screen displays, light emitting diodes, and the like.
Various alternative TCMs have been explored, including, by way of example, networks of carbon nanotubes (“CNTs”), networks of metal nanowires (“NWs”), and chemical vapor deposited (“CVD”) polycrystalline graphene (“poly-graphene” or “PG”) films. While these potential ITO replacements each resolve several practical issues associated with ITO, their respective RS-T curves are not significantly different from that of ITO (as shown in FIG. 9). For instance, to achieve technologically relevant sheet resistance values (e.g., RS<20 Ω/sq), the density of a network of CNTs or NWs must significantly exceed the percolation threshold. These high densities of CNTs or NWs, however, reduce the transmittance of such TCMs considerably. Moreover, even with low RS, vertical current collection in PV cells is compromised by current crowding at the small-area interface between a network of CNTs or NWs and the bulk emitter layer. Meanwhile, experimental data suggests that there is a fundamental limitation to the sheet resistance and transmittance of pure poly-graphene films, making it difficult for poly-graphene to compete successfully with ITO.